1. Field of the Invention
The present invention relates to a method and an apparatus for preparing a fluorine-based solvent and, more specifically, the present invention relates to a method and an apparatus for preparing a purified fluorine-based solvent useful for the production of various functional elements having on the surface thereof a lubricant layer, and also relates to a lubricant composition and a cleaning agent composition. The lubricant composition of the present invention can be advantageously applied to a magnetic recording layer of a magnetic disk (magnetic recording medium) for use in a hard disk device or the like of computers and to a carbon protective coating for protecting a magnetic head. The term xe2x80x9cfunctional elementxe2x80x9d used herein means an element designed particularly for a magnetic disk device, such as magnetic disk and magnetic head, or any elements having a lubricant layer capable of exhibiting a certain function.
2. Description of the Related Art
In the field of information processing devices such as computers, a magnetic disk device is widely used as an outer memory unit. When a magnetic disk device is used, the recording or reading of information on a magnetic disk can be performed by moving a magnetic head over the magnetic disk. To cope with recent requirements (for example, recording and reading with high density, high sensitivity and high speed), various improvements have been made on the structure or material of the magnetic disk.
With the progress of high density recording on a magnetic disk, pollution on the disk surface causes a serious problem. More specifically, if a pollutant adheres to the disk surface, the pollutant is scattered due to rotation of the disk during the operation of the magnetic disk device, thereby causing troubles such as corrosion of the magnetic head. Various causes are considered to bring about the adhesion of pollutants, but a lubricant layer formed on the surface of the magnetic disk to attain lubrication seems to be mostly responsible. For forming the lubricant layer, a lubricant composition, obtained by dissolving, for example, a fluororesin-based lubricant in a fluorine-based solvent, is coated on the disk surface and in the preparation or coating step of this composition, trace amounts of pollutants (ionic organic materials in many cases) are incorporated into the composition from the surrounding environment. In order to solve this problem brought about by the polluted lubricant composition, the lubricant composition has been heretofore regularly inspected regarding the amount of ionic organic materials contained therein by ion chromatography and exchanged for a new lubricant composition when the amount of organic materials exceeds a previously determined standard level (upper limit). However, it is very cumbersome and costly to regularly inspect the composition and frequently exchange the used composition with a new and fresh composition. Furthermore, since the fluorine-based solvent is a very expensive chemical, the cost of the treatment is very high.
In recent years, because fluorine-based solvents are widely used in various fields, there is a movement to refining the used lubricant composition and recycling the separated fluorine-based solvent so as to reduce the cost or prevent environmental pollution. However, this purification step is disadvantageous in view of energy savings because the purification must be performed by a distillation operation which requires continuous feeding of the vaporization heat from the beginning to the end of the operation and, also, the cost necessary for the operation of the distillation apparatus increases. As a matter of more importance, this purification step cannot attain complete removal of ionic organic materials contained as a pollutant in the fluorine-based solvent and undesirable residues of the organic materials generally remain in an amount of about 60 ng/ml.
Recently, an operation of coating a lubricant on a disk surface and then rinsing the disk surface with a fluorine-based solvent to wash out the extra lubricant and thereby increase the frictional properties of the magnetic disk is often performed. In this case, the fluorine-based solvent is repeatedly used as a cleaning solution and exchanged for a fresh fluorine-based solvent when the solution is outstandingly soiled. However, according to this cleaning method, as the number of repetitions of using the fluorine-based solvent increases, the amount of pollutants (e.g., lubricant and ionic organic materials) in the solvent also increases, therefore, there arises a problem that the lubricant washed out again adheres to the disk surface and thus the resulting lubricant layer shows a varied distribution in thickness. This problem may be solved by recycling the fluorine-based solvent through distillation, however, this method has the problem described above.
The object of the present invention is to solve the above-described prior art problems and provide a method and an apparatus for preparing a fluorine-based solvent useful in providing a lubricant composition which is advantageously used in the formation of a lubricant layer on the surface of a functional element such as magnetic recording medium, contains only in a negligible amount of pollutants capable of adversely affecting on the surrounding environment, is inexpensive, and can be easily recycled.
These objects and other objects of the present invention will be easily understood from the following detailed description of the preferred embodiments of the present invention.
The present inventor has found that for removing a trace amount of impurities (ionic organic materials) contained in a fluorine-based solvent and impurities such as residual lubricant from the fluorine-based solvent, it is very effective to introduce and pass the fluorine-based solvent into and through an appropriate adsorbent and allow the adsorbent to selectively trap only impurities.
In one aspect thereof, the present invention resides in a method for preparing a purified fluorine-based solvent from a fluorine-based solution comprising a lubricant based on a fluororesin having an organic group at the terminal of the resin structure and a fluorocarbon-based solvent, comprising an adsorption step of selectively removing impurities including ionic pollutants contained in the fluorine-based solution and the lubricant, by an adsorption process.
In another aspect thereof, the present invention resides in an apparatus for preparing the purified fluorine-based solvent, as mentioned above, comprising an adsorbing station filled with an adsorbent capable of trapping impurities including ionic pollutants contained in the fluorine-based solution and the lubricant, disposed on the way of passage of the fluorine-based solution.